| Soil moisture is the basic condition for carrying out agricultural activities.Water transport influences soil properties and root distribution characteristics,providing pathways for water transport;correspondingly,root distribution in the soil changes soil properties.As a result of land use changes,a series of changes in soil physical and chemical properties and plant root distribution characteristics have occurred.Soil hydrological transport is affected by the combined effect of soil properties and root structure.Different plant root configurations and soil physicochemical properties can cause the hydrological connectivity of the profile to reflect different trends.In response to the national policy of returning farmland to forests and converting slopes to terraces,slope conversion to terraces has become one of the main soil and water conservation measures to improve the fragile ecological environment in mountainous areas;influenced by economic development,citrus industry is one of the most representative warfarin development industries in the Three Gorges reservoir area.In this study,we quantified the hydrological connectivity of soil profiles through dye tracing tests,and analyzed the interrelationship between plant roots,soil properties and hydrological connectivity of profiles.The study of soil root structure and soil water transport in purple soils can help to understand the soil water transport pattern and its influencing factors under the typical agricultural use changes in the region,and provide a theoretical basis for further understanding the ecohydrological mechanism of the watershed.The main findings of the paper are as follows.(1)The structural characteristics,distribution and soil properties of root systems in cultivated land and orchards were different.The root system of maize in the cropland was mainly concentrated in the depth range of 0-10 cm,accounting for 90.09%of the total root system,and the root distribution depth was limited,and the root biomass showed an overall decreasing trend with the increase of soil depth.Citrus roots in the orchard were mainly distributed in the depth range of 0-50 cm,but there were differences in the total number and distribution of roots.The root biomass in the paddy field to orchard was 3.05 times higher than that in the dryland to orchard,and the root biomass in the dryland to orchard first decreased and then increased with the increase of soil layer depth.The soil texture of the cultivated and paddy field to orchards was loamy,and the soil at the 0-10 cm level of the paddy field to orchard had better aeration and permeability,high saturated soil hydraulic conductivity,and high total and non-capillary porosity;the dryland to orchard was a sandy loam with high soil gravel content,with a mean value of 15.63%.(2)The hydrological connectivity of soil profiles from large to small were dryland to orchards(2490.94cm~2),paddy field to orchard(1524.63cm~2)and cultivated land(1054.92cm~2).The distribution characteristics of the hydrological connectivity areas of the arable land and orchard profiles differed significantly,and there was a significant correlation between the spatial variation of the root system and the hydrological connectivity of the soil profile,and the degree and variation of the hydrological connectivity of the soil profile of the same plant root system had some similarity.The high hydrological connectivity zone of the cultivated land was mainly distributed in the soil from0 to 20 cm,which was consistent with the main distribution depth range of the maize root system;while the water connectivity depth of the orchards were influenced by the distribution range of the citrus root system,and the difference in the occurrence degree of hydrological connectivity was not significant.With the increase of distance from trees,the hydrological connectivity of soil profile of paddy field to orchard gradually decreased,and the higher content of gravel affected the hydrological connectivity of soil profile in dryland to orchard compared with paddy field to orchard.(3)The differences in root biomass and architectural characteristics are the main reasons for the spatial heterogeneity of the hydrological connectivity of the profiles,and the hydrological connectivity of the profiles is higher in the root-enriched regions.The root biomass,root length,root surface area and root volume density are higher in the high hydrological connectivity area,and the root system can form a large number of pores with better connectivity,which can effectively conduct soil water and nutrients.The difference of soil properties determines the degree of hydrological connectivity of the soil profile.The soil with good ventilation and water permeability has a higher hydrological connectivity of the profile.The soil bulk density in the high hydrologically connected area is smaller than that in the low hydrologically connected area,and the total porosity,saturated hydraulic conductivity and soil nutrient content are slightly higher than those in the low hydrologically connected area.(4)The hydrological connectivity of the soil profile was influenced by a combination of multiple factors.The results of the principal component analysis showed that plant root structure,soil physical properties,and organic matter were the three factors affecting the hydrological connectivity of the soil profile,among which plant root structure was the most important factor,explaining 66.30%of the variance variation.Soil physical properties,which reflect the condition of soil pore space,explained 20.13%of the variance variation,and plant-related soil environmental factors were influenced by plant root structure,which had an impact on the hydrological connectivity of the soil profile. |
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